Inhaled hydrogen gas therapy for prevention of noise-induced hearing loss through reducing reactive oxygen species.
水素ガス吸入による騒音性難聴の予防：活性酸素種の低減を介した内耳保護効果
Abstract
Reactive oxygen species (ROS) generated in the inner ear are central to the development of noise-induced hearing loss (NIHL). This animal study investigated whether H2 gas inhalation could mitigate NIHL in guinea pigs exposed to noise, followed by daily 5-hour inhalation of 0.5%, 1.0%, or 1.5% H2 for five consecutive days. Auditory brainstem response measurements showed that threshold shifts improved significantly in the 1.0% and 1.5% H2 groups relative to untreated controls. Outer hair cell (OHC) survival assessed 7 days post-exposure was markedly higher in the 1.0% and 1.5% groups, particularly in the basal cochlear turn. Immunohistochemical staining for 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, revealed substantially reduced immunoreactivity in H2-inhaled animals compared with controls. These findings indicate that H2 inhalation at concentrations of 1.0% and above confers meaningful protection against noise-induced cochlear injury through ROS suppression.
Mechanism
Inhaled H2 selectively scavenges ROS produced in the inner ear following noise exposure, reducing oxidative DNA damage (measured by 8-OHdG immunoreactivity) in outer hair cells and thereby limiting cochlear injury.
Bibliographic
- Authors
- Kurioka T, Matsunobu T, Satoh Y, Niwa K, Shiotani A
- Journal
- Neurosci Res
- Year
- 2014
- PMID
- 25196919
- DOI
- 10.1016/j.neures.2014.08.009
Tags
Delivery context
In air, molecular hydrogen is reported to be combustible across approximately **4% (LFL, lower flammability limit) to 75% (UFL, upper flammability limit)**. Among high-concentration hydrogen inhalers, 66% output sits inside this range, and even pure-hydrogen (100%) output forms a 4–75% concentration-gradient layer at the device–air boundary (the UFL 75% paradox). Engineering principle would therefore call for operation below LFL (the classical 4%); that figure, however, was measured under closed, pre-mixed, static conditions. For the open, dynamic inhalation environment, the empirical value reported in the literature is **10%**, which is the figure referenced in practice as the operating ceiling. The 66% / 100% output devices are recorded in the Japanese Consumer Affairs Agency accident-information database, and from these considerations are not recommended.
Safety notes
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